Laminated safety glass



July 30, 1940- I' G. B.- wATKlNs ET AL l 2.209,435

LAMINATED SAFETY GLASS Filed Nov. 15, 1935 Fatented July 3G, 1 i' i i;

rse E. `Wat and d Ohio, ignore to lhihmynllln-hord G Gom, '.ioledo9 @lila a poration or @his .application November l5, i935, l No. dial? tween the pyroxylin plastic and glass, there have been but a limited number of mediums capable of giving commercial adhesion between glass and plasticizer is added giving an adhesive capable of. commercial use in the manufacture of laminated safety glass composed of glass and cellulose acetate plastic laminations.

The adhesive produced in accordance with this invention not only has adhesive properties toward glass but is alsosuclently compatible with the cellulose acetate plastic sheet to give a lamination of good clarity and stability.

In the drawing:

Fig. l is a diagrammatic showing of the spray- 40 lng of our improved adhesive upon a sheet of glass;

Fig. 2 ls likewise a diagrammatic showing illustrating the application of the adhesive to the glass by means of a coating machine;5

Fig. 3 illustrates the drying of. the adhesive A film after it has been applied to one surface of a sheet of glass; A

Fig. 4 is a sectional view showing the coated Aglass, sheets and layer of cellulose acetate plastic in proper superimposed relationship but out of contact with one another for sake or clearness; Fig. 5 illustrates dlagrammatically a platen type of press which may be used to eect inlti bonding of the lamlnations; Fig. 6 is a vertical sectional view or an ordinary mations can be eected; and

Fie. 7 is a. sectional view through a sheet of -finished laminated safety glass.

lle the condensation product of a partially y hydrolyzed polyvinyl acetate and formaldehyde may compoded in a number of diderent ways, by way of. example we suggest that one mole or poly vinyl acetate of the desired viscosity be dissolved in about500 c.- c. of glacial acetic acid. This solutionV is heated to the boiling point and just as much water is added as can be tolerated without causing precipitation of the resin.

Following this step, the mixture is vthen reuxed and from .time to time an analysis is made of t-he acetyl value in order to determine the extent to which the resin has been hydrolyzed. We prefer that the percent hydrolysis (which can l ar= rested at any desired point) be carried to within the range of approximately to 95% hydrolysis as this is a satisfactory range for most cellulose acetate plastic sheets; that is, an adhesive made' from a poly vinyl acetate which has been hydrolyzed to the extent of 75% to 95% will be adequate for the ordinary commercial cellulose acetate plastic obtainable. Additional water may be added tothe mixture during reiiuxing to ac= celerate hydrolysis.

The partially hydrolyzed poly vinyl acetate is' then recovered in any suitable fashion such as by pouring into water, ltering,and ng, or the acetic acid and water mixture can be distilled ed in vacuo.

After recovering the partially hydrolyzed -poly vinyl acetate, it is reacted with formaldehyde the degree of partial hydrolysis of the poly-vinyl acetate and the composition of the cellulose acetate-plastic which is to be bonded to the glass.

The reaction product is then plasticlzed with such plastlcizers as the phthalate esters includine dimethyl phthalate, dlethyl phthalate, etc.

For use as a spray adhesive coat, l0 parts of the reaction product of the partially hydrolyzed poly vinyl acetate and formaldehyde was dlssolved in 260 parts of ethyl acetate (volatile solvent) and`4 parts of dimethyl phthalate (plasticlzer). The solution was then sprayed on glass sheets (see sheet 10, Fig. l) by means of a 'gun il to form the nlm of adhesive l2. To remove the volatile solvent from the deposit I2 on the glass, the coated glass is subjected to slightly elevated temperatures, and as shown diagram' matically the coated glass sheet it in Fig. 3 is placed on a heated platen it. In this particular operation, the upper platen l5 is not brought v into contact with the adhesive layer on the glass, the sole purpose of placing the glass in the platen press being to heat the same and to drive ofl? the volatile solvent. In our Work, the coated glass sheet was subjected to a temperature of 250 F. for a few minutes.

- After two of such sheets oi glass have been treated, a sheet of cellulose acetate plastic IS is interposed as shown in Fig. 4. The sandwich thus formed is then subjected to an initial pressing which can be accomplished by means of a platen press such as that illustrated diagram' matically by the numeral i1. The sandwich between the platens of the press may be pressed for a period f three minutes at a pressure of 100 pounds per square inch and at a temperature of 250 F.

.As most satisfactory results can ordinarily be had by subjecting the sandwiches to hydraulic pressure to effect nal compositing, the preliminarily pressed sandwiches; it are given a final pressing treatment in an autoclave i9. As shown diagrammatically, the sandwiches are carried in a rack 20 adapted to be placedin the autoclave and when closed the temperature and pressure of the fuid 2i is so controlled as tc subject the glass to a cycle of about 250 pounds per square inch at a temperature of approximately 300 F. and for a period of about five minutes.

Upon removal from the autoclave, it will be found that the glass and cellulose acetate plastic laminations have been permanently bonded together by means of our improved resin type adhesive. To positively protect the bond between the laminations as well as the cellulose acetate plastic lamination, the marginal portions thereof may be removed to create a channel in which a Weather-proofing material can be inserted to form the seal 22 shown in Fig. 7.

In lieu-of the spraying method disclosed in Fig. 1, the adhesive can be made of roll coating consistency, and as shown in Fig. 2, a supply of adhesive 23, made by dissolving parts of the reaction product of partially hydrolyzed poly vinyl acetate and formaldehyde resin in 100 parts of carbitol acetate (or a mixture of 50 parts of cellosolve acetate and 50 parts of carbitol acetate) and 4 parts of dimethyl phthalate, is contained in the hopper 2d having the controllable discharge orifice 25. The adhesive flows upon the series of rolls 26 and by passing the sheet of glass 2l between the rolls 28 and 2Q, the layer of adhesive 30 is deposited upon the uppersurface of the glass.

-materially in physical properties depending upon the type of cellulose acetate used in preparing the plastic sheet. This variation is not only effected by the viscosity of the'raw cellulose acetate but is influenced by the acetyl content, solubility,

etc. aswell. Therefore, in producing our adhesive, it should be borne in mind that slight variations may be required in proportions. 'In all cases, however, the adhesive material should remain compatible with the cellulose acetate plastic as well as adhesive toward glass surfaces. With this control, proper adhesion will be had as well as satisfactory transparency in the finished laminated structure.

We claim: A

l. Laminated safety glass comprising two sheets of glass and an interposed layer of transparent cellulose acetate plastic bonded to said glass sheets with a compatible adhesive formed from the condensation products of a partially hydrolyzed polyvinyl acetate and formaldehyde plasticized with an ester of phthalic acid which is compatible with the adhesive and also with the transparent cellulose acetate plastic.

2. Laminated safety glass comprising two sheets of glass and an interposed layer of transparent cellulose acetate plastic bonded to said glass sheets with an adhesive formed from polyvinyl acetate hydrolyzed to the extent of from about '75% to 95% reacted with formaldehyde in the approximate proportions of one mole of partially hydrolyzed polyvinyl acetate to one mole of formaldehyde," and having mixed therewith an ester of phthalic acid plasticizer compatible with both the reaction product and the transparent cellulose acetate plastic.

GEORGE B.. WATKINS. JOSEPH D. RYAN. 

